National Institute Of Materials Physics - Romania

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5781 articles found

3321. Microstructure of MgB2 samples observed by x-ray microtomography

Authors: Badica, P; Aldica, G; Craciunescu, T; Tiseanu, I; Ma, Y; Togano, K

Published: NOV 2008, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 21, DOI: 10.1088/0953-2048/21/11/115017

It is shown that x-ray microtomography (XRT) is a powerful technique to observe on extended volumes the morphology, alignment and local bulk density in MgB2 tapes, thin films and especially bulk specimens. For the bulk samples obtained from mechanically milled powders for different conditions, several types of the 3D microstructural patterns were observed. These significant differences between the samples were not revealed by SEM. Microtomography can be a useful additional technique to characterize the samples and to obtain unique information, e. g. on local bulk density, but it cannot replace the existing methods: advantages and limitations are discussed. It is concluded that the method is promising and further developments are expected to be helpful for a better understanding of the complex processing-microstructure-properties relationship in the MgB2 superconductor.

3322. Comparative Study on the Microstructural and Magnetic Properties of Cobalt Ferrites Synthesized by Ceramic and Oxidation Wet Methods

Authors: Feder, M; Diamandescu, L; Bibicu, I; Caltun, OF; Dumitru, I; Boutiuc, L; Chiriac, H; Lupu, N; Vilceanu, V; Vilceanu, M

Published: NOV 2008, IEEE TRANSACTIONS ON MAGNETICS, 44, 2939, DOI: 10.1109/TMAG.2008.2002200

CoFe2O4 and CoMn0.2Fe1.8O4 ferrites were synthesized using standard solid state phase ceramic method and coprecipitation and oxidation method. X-ray diffraction, Mossbauer spectroscopy, and surface electron microscopy were used to characterize the samples' microstructures. Vibrating sample measurement and strain gauge technique were used to characterize the magnetic and magnetostrictive properties of both powders and sintered samples, respectively. The specific magnetization increased from 55 emu/g for stoichiometric ferrite samples obtained by conventional method to 179 emu/g for coprecipitated ferite powders respectively. In the manganese substituted cobalt ferrite case the specific magnetization increased only twice, from 77 emu/g to 168 emu/g. The maximum magnetostrictive coefficient of coprecipitated samples of 145 ppm is smaller compared to that of solid state phase ceramic samples of 195 ppm. The most important benefit in the case of the coprecipitated and oxidized samples is the four fold increase of the maximum strain derivative compared to solid state phase ceramic samples.

3323. InN thin films deposited on flexible substrates by reactive RF-magnetron sputtering

Authors: Zoita, NC; Besleaga, C; Braic, L; Mitran, T; Grigorescu, C; Nedelcu, L

Published: NOV 2008, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 2, 720, DOI:

Indium nitride is an attractive semiconductor material for optoelectronic applications, high-speed electronics and solar cells. We report successful deposition of polycrystalline InN thin films onto kapton polyimide flexible substrates by reactive RF magnetron sputtering method. The optical, structural and morphological characterization data are presented.

3324. Synthesis and characterization of star and brush grafted polysiloxanes, obtained by atom transfer radical polymerization

Authors: Nor, I; Sandu, V; Ibanescu, C; Hurduc, N

Published: OCT 30 2008, E-POLYMERS, DOI:

Star- and brush-polysiloxanes were synthesized via living radical polymerization using two different catalytic systems. The new compounds were characterized by H-1-NMR, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) techniques. CuCl and 2,2'-bipyridyl proved to be the most efficient catalytic system. The type of catalytic system and the reaction conditions control the number of arms for star polymers or the grafted-chain density for brush polymers. The use of chloromethyl styrene as monomer or co-monomer yields homogeneous star- or brush-polysiloxanes, although chloromethyl styrene is an inimer system. The homogeneity of materials was verified by GPC and DSC (TOPEM) methods. For linear grafted polysiloxanes the molecular simulations reflect a tendency of chains to adopt globular conformation for high values of the branching density. The polysiloxanes grafted with styrene/chloromethyl styrene were modified with azobenzene in order to obtain systems able to react to the light stimuli. Rheological behavior of the polymer solutions were evaluated before and after irradiation with UV light. After the UV irradiation a significant viscosity increase was evidenced.

3325. Superparamagnetic nanomagnetites modified with histidine and tyrosine

Authors: Culita, DC; Marinescu, G; Patron, L; Carp, O; Cizmas, CB; Diamandescu, L

Published: OCT 15 2008, MATERIALS CHEMISTRY AND PHYSICS, 111, 385, DOI: 10.1016/j.matchemphys.2008.04.033

Magnetite nanoparticles coated with tyrosine and histidine were synthesized by in situ decomposition of the precursors-coordination compounds containing the aminoacids as ligands. All of the obtained compounds were characterized using infrared spectroscopy (FTIR), X-ray diffraction, Mossbauer spectroscopy, magnetic and thermal measurements. Data demonstrate the presence of the aminoacids chemisorbed on the surface of magnetite nanoparticles and their superparamagnetic character. (C) 2008 Elsevier B.V. All rights reserved.

3326. Studies on multifunctional textile materials. Plasma deposition onto textile materials and onto reference plates

Authors: Beica, T; Nistor, LC; Morosanu, C; Frunza, L; Stan, GE; Zgura, I; Marcov, D; Dorogan, A; Carpus, E

Published: OCT 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2817, DOI:

The magnetron sputtering method was used to obtain layers of indium tin oxide or hydroxyapatite on glass fiber woven and on reference glass plates. The layers were characterized by scanning microscopy, UV-vis spectroscopy and conductivity measurements. Hydrophilic properties of the woven samples were investigated by optical microscopy following the behavior of a water droplet upon the each of the samples. The change of the drop profile in time due to wetting of the fabric leads to the wetting kinetics. The most efficient treatments to improve the hydrophilic/wetting properties of the glass fiber woven were found.

3327. Nanospinel mixed oxides obtained by self-propagating combustion. Blue cobalt aluminate

Authors: Suciu, C; Mindru, I; Marinescu, G; Patron, L; Carp, O; Teodorescu, VS

Published: OCT 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2707, DOI:

Blue cobalt aluminate was obtained by self-propagating combustion from the system 2Al(NO3)(3)center dot 9H(2)O : 1Co(NO3)(2)center dot 6H(2)O : nNH(2)CH(2)COOH. The precursor was characterized by elemental chemical analysis, IR and UV-Vis spectra and thermal analysis. The CoAl2O4 spinel was characterized by the X-ray diffraction, TEM, IR and UV-Vis spectra.

3328. Non-covalent functionalization of carbon nanotubes: Experimental evidence for isolated and bundled tubes

Authors: Husanu, M; Baibarac, M; Baltog, I

Published: OCT 2008, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 41, 69, DOI: 10.1016/j.physe.2008.06.001

Single-walled carbon nanotubes (SWNTs) may be used in technological applications as individual entities instead of bundled tubes. The Raman signature of these two forms is still a controversial subject. The profile, peak position and relative intensity of the Raman band associated with the tangential vibration modes (G band similar to 1600cm(-1)) and radial vibration modes (RBM similar to 100-200cm(-1)) are the main parameters which can reveal the dispersion state of nanotubes. Resonant Raman scattering and absorption spectroscopy on SWNTs furnish complementary information concerning the efficiency of the nanotube dispersion in individual entities. (C) 2008 Elsevier B.V. All rights reserved.

3329. Single-beam pumped coherent anti-Stokes Raman scattering on carbon nanotubes

Authors: Lefrant, S; Buisson, JP; Mevellec, JY; Baltog, I; Baibarac, M

Published: OCT 2008, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 245, 2224, DOI: 10.1002/pssb.200879567

Giant optical fields locally generated in nanoscale metal structures through the local excitation of surface plasmons underlie a variety of nonlinear optical processes. Using silver and gold rough metallic films, reproducible enhancements of the Raman signal on various materials including carbon nano-tubes have been demonstrated. In addition, an abnormal anti-Stokes Raman emission, reminiscent of Coherent anti-Stokes Raman Scattering (CARS), is accurately observed on nano-metric thin films. We demonstrate that under a tight focusing of the excitation light, a CARS-type emission, resulting from a wave mixing process between the incident laser light and Stokes Raman light generated by a SERS mechanism, is produced. The results which corroborate the CARS emission are the following: a square relation between the CARS signal intensity and the film thickness; a square relationship between the CARS signal intensity and the exciting laser intensity; a dependence of the CARS intensity on the numerical aperture (NA) of the microscope objective used for the detection of the anti-Stokes signal; a polarization ratio in the anti-Stokes side always greater in comparison with that measured for an usual Stokes Raman signal. We demonstrate also that this mechanism may contribute to a clear identification of the state of the observed nanotubes, i.e. in isolated or bundled forms, even when tubes are in powders. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

3330. Substituted cobalt ferrites for sensors applications

Authors: Caltun, O; Dumitru, I; Feder, M; Lupu, N; Chiriac, H

Published: OCT 2008, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 320, E873, DOI: 10.1016/j.jmmm.2008.04.067

The aim of this work was to study the influence of the sintering temperature and of the substitution level on the Curie temperature and on the magnetostriction coefficients for four series of cobalt ferrites sintered by conventional ceramic method. The microstructure of the samples was characterized using X-ray diffractometry and scanning surface electron microscopy. Vibrating sample magnetometry and strain gauge measurements were used to characterize the magnetic and magnetostriction properties. The study proves that a small amount of manganese substitution for iron decrease drastically the Curie temperature but in the same time decrease the specific magnetization and magnetostriction coefficient. Despite this drawback, the manganese substituted cobalt ferrites present the largest strain derivative. The maximum of the magnetostriction coefficient is also influenced by the stoichiometry of the cobalt ferrites. The magnetostriction coefficient of cobalt ferrite can be enhanced by substitution of small fraction of iron or cobalt by silicon or manganese, this implying the modification of the strain derivative as well as magnetostriction at lower magnetic fields. The maximum magnetostriction can be tuned by substitution levels and sintering parameters. (C) 2008 Elsevier B.V. All rights reserved.